The present invention relates generally to display systems, and more particularly, to a display system operable to use either ambient light or light from a dedicated light source.
Display systems typically include a display surface having an array of pixels for displaying data or images in accordance with signals generated by an image control circuit. The display surface may comprise, for example, a liquid crystal display (LCD) panel, or any other spatial light modulator (SLM) which reflects or transmits light produced eternally. The display system may be a microdisplay for use with a computer, head mounted display, handheld device, or any other device having a display screen for displaying images. Conventional display systems include a dedicated light source to illuminate the display surface. The display screen is, however, often located within a well lighted area. It would be desirable to utilize ambient light when the ambient light is sufficiently bright to produce an image. This would allow the display system to conserve energy and increase the useful life of the light source. However, conventional optics for directing ambient light onto a display are typically complex and require too much space to use with compact display systems based on microdisplays.
There is, therefore, a need for compact display system operable to switch between ambient light and light from a light source of the display system.
A display system of the present invention generally comprises a display device operable to display an image and configured for illumination by ambient light or light emitted by a dedicated light source. The display system further comprises a light directing system operable to direct one of the ambient light and the light emitted by the light source towards the display device. The light directing system comprises at least one holographic optical element which is switchable between an active state wherein light incident on the element is diffracted and a passive state wherein light incident on the element is transmitted without substantial alteration.
The display device may be transmissive or reflective and is preferably mounted on one end of a light guide. The light directing system may comprise a reflective holographic optical element and a transmissive holographic optical element, for example.
In another aspect of the invention, a display system generally comprises a display device operable to display an image, a light source, and a light directing system. The light directing system is operable is switchable between an ambient light mode wherein the display device is illuminated by ambient light and an internal illumination mode wherein the display device is illuminated by the light source. The light directing system comprises at least one holographic optical element.
The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, drawings, and claims.